Performance of an Ultra-Sensitive Assay Targeting the Circulating Anodic Antigen (CAA) for Detection of Schistosoma mansoni Infection in a Low Endemic Area in Brazil

Abstract

Techniques with high sensitivity and specificity are required for an accurate diagnosis in low-transmission settings, where the conventional parasitological methods are insensitive. We determined the accuracy of an up-converting phosphor-lateral flow circulating anodic antigen (UCP-LF CAA) assay in urine and serum for Schistosoma mansoni diagnosis in low-prevalence settings in Ceará, Brazil, before and after praziquantel treatment. Clinical samples of a total of 258 individuals were investigated by UCP-LF CAA, point-of-care—circulating cathodic antigen (POC-CCA), soluble worm antigen preparation (SWAP)-ELISA and Kato-Katz (KK); a selection of 128 stools by real-time PCR technique. Three and 6-weeks after treatment, samples were collected and evaluated by detection Schistosoma circulating antigens (CAA and CCA). The UCP-LF CAA assays detected 80 positives (31%) with urine and 82 positives (31.8%) with serum. The urine POC-CCA and serum SWAP-ELISA assays detected 30 (11.6%) and 107 (40.7%) positives, respectively. The Kato-Katz technique revealed only 4 positive stool samples (1.6%). Among the 128 individuals with complete data records, 19 cases were identified by PCR (14.8%); Sensitivities and specificities of the UCP-LF CAA assays, determined versus a combined reference standard based on CCA/KK/PCR positivity, ranged from 60–68% to 68–77%, respectively. In addition only for comparative purposes, sensitivities of the different assays were determined vs. a comparative reference based on CAA/KK/PCR positivity, showing the highest sensitivity for the urine CAA assay (80%), followed by the serum CAA (70.9%), SWAP-ELISA (43.6%), PCR (34.5%), POC-CCA (29.1%), whilst triplicate Kato-Katz thick smears had a very low sensitivity (3.6%). CAA concentrations were higher in serum than in urine and were significantly correlated. There was a significant decrease in urine and serum CAA levels 3 and 6-weeks after treatment. The UCP-LF CAA assays revealed 33 and 28 S. mansoni -infected patients at the 3- and 6-week post-treatment follow-up, respectively. The UCP-LF CAA assays show high sensitivity for the diagnosis of S. mansoni in low-endemicity settings. It detects a considerably higher number of infections than microscopy, POC-CCA or PCR. Also it shows to be very useful for evaluating cure rates after treatment. Hence, the UCP-LF CAA assay is a robust and promising diagnostic approach in low-transmission settings.

Evaluation, Validation, and Recognition of the Point-of-Care Circulating Cathodic Antigen, Urine-Based Assay for Mapping Schistosoma mansoni Infections

“…These urine samples were sent to Leiden University Medical Center (LUMC) to be further tested by the very sensitive and schistosome-specific up-converting phosphor lateral flow circulating anodic antigen (UCP-LF CAA) assay. 21 In this selected subset, the average prevalence levels by KK, POC-CCA, and UCP-LF CAA were 6.8%, 53.5%, and 46.5%, respectively. Sixty-one percent of the positive POC-CCA readings were traces.…”

“…Based on the LCA studies of the data from the SCORE mapping in Burundi and Rwanda, approximately 50% 20,22 or at least 50% of the trace POC-CCA readings were estimated to be true positives. [20][21][22] In mapping settings like these, where MDA had been going on for only 6 or 7 years and prevalence is low by the KK assay but high by POC-CCA, we propose categorizing trace results as positive. This would ensure treatment is provided to people in areas that would benefit by treatment but that would be excluded based on KK mapping.…”

Circulating Anodic Antigen (CAA): A Highly Sensitive Diagnostic Biomarker to Detect Active Schistosoma Infections—Improvement and Use during SCORE

“…Application of the SCAA500 test improved detection of low-level infections in travelers 15 and substantially improved detection sensitivity in low endemicity settings. [18][19][20][21][22] MODIFYING THE TEST FOR USE WITH URINE Clearance of CAA from the bloodstream occurs at least partly via the kidneys, 23,24 suggesting urine specimens could potentially be used for assessing infection status. The CAA-ELISA test yielded low sensitivity when used on urine samples compared with serum, in part due to lower CAA concentrations in urine.…”

“…It seemed clear that multiple other field-based studies could benefit from the advancements in the high-sensitivity urine-based CAA assay. Countries where the assay has been used include Brazil, 19 Cambodia and Lao People's Democratic Republic, 22 People's Republic of China, 20 and Tanzania. 29 These studies mainly focused on endemic settings where prevalence and intensity of infection (whether with S. mansoni, S. haematobium, Schistosoma japonicum, or Schistosoma mekongi) was very low or transmission was thought to have been interrupted.…”

“…With respect to clinical sensitivity, the SCAA20 performs comparably to the UCAA250 28 and the SCAA500 compares with the UCAA2000 assay. 19 , 21 The latter two assays approach the sensitivity needed to possibly detect infection with a single worm or worm pair. Whether to test serum or urine is, in part, dependent on the circumstances.…”